Time Division Duplex (TDD) is a radio transmission mode on radio channels. In the TDD mode, the transmission and reception are conducted in a time division manner, that is, the radio transmission based on the TDD mode realizes the time division multiplexing of uplink and downlink channels. The TDD mode is implemented by repeating Time Division Multiple Access (TDMA) frame structures periodically in time domains. For example, in Long Term Evolution (LTE), the 3GPP LTE has two TDD frame structures. The first frame structure is as shown in FIG. 1, in which a radio frame is composed by 20 slots, a period of a frame is 10 ms, and every two slots form a subframe (SF). The second frame structure is as shown in FIG. 2, in which a period of a frame is also 10 ms, a frame is divided into two half-frames, each half-frame is composed by seven SFs, a guard interval is inserted between every two SFs, and a guard period (GP) is formed by a downlink pilot time slot (DwPTS), a GP, and an uplink pilot time slot (UpPTS).
In the frame structure in the TDD mode, one frame includes several SFs or slots. The SFs may be classified into uplink SFs and downlink SFs, and a TDD system may use a transfer point to change the SF types flexibly. For example, the current 3GPP LTE standard specifies various SF ratios in the two frame structures. FIG. 3 is a schematic view of various uplink and downlink SF ratios in the first frame structure, in which the ratios in one frame are illustrated. FIG. 4 is a schematic view of various uplink and downlink SF ratios in the second frame structure, in which the ratios in one and a half frames are illustrated. A table of uplink and downlink SF ratios (as shown in Table 1) can be concluded from FIGS. 3 and 4. Table 1 lists the situation of one transfer point, that is, the situation that the uplink and downlink SFs have only one type transfer.
TABLE 1Uplink and Downlink SF RatiosFrame Structure(Downlink:Uplink)First Frame Structure4:1, 3:2, 9:1, 6:4, 7:3, 8:2, 10:0,2:2, 4:2, 2:3, 1:4Second Frame Structure6:1, 5:2, 4:3, 3:4, 2:5, 1:6
According to different service requirements, the TDD system needs to indicate the uplink resources to which some uplink instructions are directed in the uplink instructions. For example, in downlink transmission of a 3GPP Evolved Universal Terrestrial Radio Access (E-UTRA) system, an Orthogonal Frequency Division Multiplexing (OFDM) technology is employed to realize multiple access. The OFDM is a multi-carrier communication technology. In a multi-carrier communication system, different time domain and frequency domain resources are granted to different users to realize multiplexing of time-frequency resources by multiple users. Here, the time-frequency resources may be granted by carrying resource grant indications of corresponding uplink SFs (ul grant) in downlink control signaling of a user. A ul grant may contain different contents. Table 2 lists the content of a ul grant.
TABLE 25 MHzULOccupiedDomainBitsContentResource Grant9Continuous physical resource blocksgranted to a userTransmission Format7Transmission format indication,Indication/Transmission Block Size +modulation and information bits numberModulation Code Formatand code formatsHybrid Automatic Retransmission2Synchronous HARQ: 2-3 bits of serialRequest (HARQ)number and implicit confirmation ofprevious transmission blocksPower Control2Relative instructionsPilot Instruction1Whether the pilot appears in the lastlong block (from other user terminals)or whether the last long block isconfigured to transmit dataChannel Quality Indication1The quality indication report about thechannel scheduling should be includedin the dataACK/NACK Indication1Indicating that the user terminal shouldreserve resources for ACK/NACK onthe physical uplink synchronous channelMulti-antenna Technology2Determined by multi-user MIMO anduplink multi-antenna technology, 2 bitsUser Terminal Identity + Cyclic2016-24-bit CRCRedundancy Check (CRC)
Generally, a base station (BS) adopts downlink SFs to send the ul grant as shown in Table 2. After receiving the ul grant, each user determines whether the user identity in the ul grant is consistent with the identity of each user itself; and if they are consistent, the resources are allocated according to the ul grant. Thus, the resources can be granted to all users. For a user, when the downlink SFs are more than the uplink SFs, each of the downlink SFs is mapped to one uplink SF, that is, the downlink SF may be configured to send a ul grant for one uplink SF. However, the frame structure in the TDD system may be asymmetrical in terms of the uplink and downlink ratio, as shown in Table 1, that is, one downlink SF may be corresponding to multiple uplink SFs, so that the corresponding uplink SF cannot be determined according to one ul grant. In this case, a downlink SF needs to be configured to send multiple ul grants, so that one downlink SF is corresponding to multiple uplink SFs, and the ul grants will be sent separately. In other words, for the same user, if it is determined that n uplink SFs are required after scheduling, n corresponding ul grants exist, which will be transmitted repeatedly. Thus, the information such as the user identity is also repeatedly transmitted for n times, resulting in the waste of transmission resources such as signaling and channels.
It is known from the above analysis that the existing method for implementing uplink resource indication in the TDD system cannot indicate the uplink resources corresponding to the ul grants precisely, which may cause the waste of the resources and lead to a low utilization of the resources.